The number of valence electrons in a group ________________ when we are moving down.

Correct option is C

Sol: The correct answer is (c) remains constant

Key Points:

All elements in the same group of the periodic table have the same number of valence electrons. This is because their electronic configurations end in the same pattern, differing only in the principal energy level (or shell). For example:

• Group 1: All elements like lithium (Li), sodium (Na), and potassium (K) have 1 valence electron.
• Group 2: All elements like beryllium (Be), magnesium (Mg), and calcium (Ca) have 2 valence electrons.

Information booster:

Valence Electrons: 

• Valence electrons are the outermost electrons responsible for chemical properties. In a group, valence electrons remain constant because elements share the same outer electron configuration. Moving down a group increases the principal energy level (n), making valence electrons farther from the nucleus.
• This results in larger atomic size, lower ionization energy, and increased metallic reactivity. For non-metals, reactivity decreases down the group. Across a period, the number of valence electrons increases, but within a group, they stay constant while energy levels increase. This explains periodic trends like atomic size, reactivity, and ionization energy.